Understanding how the brain works — The past, present, and future of brain mapping

Every human experience is profoundly shaped by how our internal processes meet halfway with the external reality of existence. This unique convergence, so influential and critical, is enabled by the activity of the human brain. For centuries, we thought to know everything about how this extraordinary organ is structured and functioning — new evidence suggests now that we might be wrong.

The past: classic neuropsychological theories on brain functioning

In his remarkable publication “Looking for Spinoza: Joy, Sorrow, and the Feeling Brain,” acclaimed Portuguese-American author and world-leading neuroscientist Antonio Damasio stated that the living brain is the brain is significantly more than just the sum of its neurons: human experience as we know emerges, instead, from the uninterrupted interaction between the brain and the environment.

The most traditional neuropsychological approach, the localizationist approach, refers to the idea that different parts of the brain are responsible for specific behaviors, or that certain functions are localized to certain areas in the brain. Studies have then identified several structures, each responsible for a separate cluster of functions, that are (or were) defined as follows.

• The parietal lobe covers a profound role in sensory perception and space, body movement, and sense of orientation. This lobe collects relevant information about sensory organs. Here pain is processed and modulated, as well as physical effort and body temperature. It enables us to understand the nature of numbers and other mathematical concepts.
• The frontal lobe represents the essence of the evolution of the human species. Located in the front of the head, just below the frontal bones of the skull, it covers different functions such as the production of language and speech and the sophisticated executive functions that allow us to plan, pay attention, memorize long-term data, understand what we see and regulate emotions.
• The occipital lobe is involved in perception and visual recognition. This structure regulates different areas of the visual field, such as identifying mental patterns to process information and send it to other areas of the brain. It makes it possible to perceive color differences and recognize familiar faces, but it also participates in processing emotions and thoughts.
• The temporal lobe is also responsible for a large number of cognitive processes. In particular, it makes it possible for us to recognize faces; it allows the articulation of language and the understanding of sounds, voice, and music. This structure is also deeply and actively involved in the modulation of emotions, such as motivation, anger, anxiety, and pleasure.
• The insular lobe seems to play an active role in the perception of taste, in the control of the bowels, and in the somatosensory system, and it would seem to be also associated with our emotional processes since it is also part of the limbic system.

The brain lobes may represent a fascinating map of processes and connections, but it is challenging to associate particular functions with each of these structures. They are interdependent, interconnected and make a perfect, distinctive balance possible. This is where the necessity of a paradigm shift emerges.

The present: innovative proposals for a new framework

Recent studies showed that there is a large degree of overlapping in the structure of complex human brain networks, associated with several well-known brain systems, such as the auditory/language, visuospatial, emotion, decision-making, social, control of action, memory/learning, and visual systems.

It is still commonly accepted that specific brain regions are crucial to enable the proper operation of each function. Cognitive functions emerge and depend on a physical brain substrate, and, in case of damage to the substrate, specific abilities may be compromised. Nevertheless, the relationship between structure and function can be far more complex than we estimated.

In fact, not only neural networks are highly overlapping, but they can often cover more than a single, unique function. Similarly, separate neural tasks can involve the integrated activity of other independent networks, as well as reconfigure networks found at rest.

In this regard, to better clarify the dynamics that exist between the brain substrate and cognitive abilities new research proposed the existence of two distinct neurocognitive axes around which brain regions would be genetically organized. The first axis would reflect the path that proceeds from basic skills, such as visual perception, up to human skills such as social cognition and abstract thinking, and would be responsible for the motivational aspects and attribution of meaning.

The second axis would deal with spatial, temporal, and movement perception. According to the researchers, this organization reflects an evolutionary path, as a similar dynamic has also been observed in non-human primates.

Those axes are not functionally independent, but they actively interact and remodel their activity based on task and context. In this fluid framework, brain structures can share their functions with other networks or cooperate with other structures as well. Brain plasticity is the fundamental ability of the brain that allows it to re-organize itself as a result of environmental pressures.

Similar evidence confirms the need for a more comprehensive framework to shift the attention from a vision of a fragmented brain and the necessity of accepting that mapping the brain by assigning specific functions to certain areas is not only highly complex but also often unsuccessful.

The future: groundbreaking implications for research paradigms

Changing the way we think about brain functional organization can provide a valuable change of perspective and positively affect not only neuropsychological research but also treatment options that will be available for patients in the near future.

Traditionally associating brain injuries with specific impairment of certain brain functions and hence, a single locus with a single function, could have limited discoveries and insights we received from neuropsychological research during the last decades.

A recent study from Stanford University is trying to overcome reductionism in neuropsychological research and neuroimaging methods. Researchers proposed that new neuropsychological paradigms should stop reducing behavior to one of its components and, instead, focus on the brain’s organizational properties and features using a computational approach, more than a localizationist one.

Shifting our attention from clusters of functions to the way tasks and features are structured and translated into neural activity can definitely expand treatment options for patients in need of neuropsychological rehabilitation and promote a more holistic approach to patient care.

Bibliography

Anderson, M. L. (2014). After phrenology: Neural reuse and the interactive brain. MIT Press.

Pessoa, L. (2016). Beyond disjoint brain networks: Overlapping networks for cognition and emotion. Behavioral and Brain Sciences, 39, E129. doi:10.1017/S0140525X15001636

Hsu CW (2016). Distinct and Overlapping Brain Areas Engaged during Value-Based, Mathematical, and Emotional Decision Processing. Frontiers in Human Neuroscience, 10, 275

Gaël Varoquaux, Russell Poldrack. (2018) Predictive models can overcome reductionism in cognitive neuroimaging.

Santarnecchi, E., Momi, D., Mencarelli, L. et al. Overlapping and dissociable brain activations for fluid intelligence and executive functions. Cogn Affect Behav Neurosci 21, 327–346 (2021). https://doi.org/10.3758/s13415-021-00870-4